There is an increasing usage of water soluble polymers and copolymers in wastewater treatment industries. These compounds have shown desirable utility for the purpose of dewatering sludge and clarifying contaminated water.
The efficacies of the polymers or copolymers used will vary depending upon the type of monomers chosen to form the polymer or copolymer, the molecular weight of the synthesized molecule and, in the case of a copolymer, the placement of the selected monomers on the backbone of the copolymer. It is the latter characteristic that is the focus of the present invention.
Polymers with long sequences of two monomers can be categorized as block copolymers or graft copolymers. In graft copolymers sequences of one monomer are "grafted" onto a "backbone" of the second monomer type, ##STR3##
Graft copolymers have unique and highly desirable properties as compared to random copolymers or the blend of two homopolymers. Therefore, there is a great interest in preparing them. Few techniques described in the literature satisfy the need.
Furthermore, with ever increasing usages of water soluble polymers and copolymers in industries such as wastewater treatment, cooling, boiler and deposit control, coating, textile, mining, detergency, cosmetics, and papermaking, etc., there is an urgent need to synthesize novel water soluble graft copolymers for this broad range of applications.
It is a further object of this invention to prepare distinctive water soluble graft copolymers for water treatment applications and specifically for papermaking processes.
U.S. Pat. No. 3,869,418 describes a graft copolymer comprising a polymeric N-vinyl lactam such as N-vinyl pyrrolidone with unsaturated carboxylic acids, like acrylic acid and methacrylic acid in an emulsion process. The resulting copolymer is not water soluble and is used for adhesive and coating applications.
U.S. Pat. No. 4,271,053 discloses quaternary ammonium graft copolymers prepared by grafting quaternary ammonium ionene-type polymeric side chains onto a polymer backbone formed by the reaction of a difunctional amine and an epihalohydrin or diperoxide. The polymers are different than the present invention.
U.S. Pat. No. 4,400,496 and European Patent Application 0 356 241 teach grafting acrylamide or acrylic acid with starch in the presence of ceric ions. The product has to be precipitated and separated in acetone prior to use.
Smirnova et. al., Journal of Polymer Science, Vol. 29, pp. 139-145 describe a graft copolymerization of methacrylic acid with polycaproamide by the persulfate/sulfite redox system in the presence of copper ions. It is a different reaction mechanism and results in a different copolymer than the present invention.
U.S. Pat. No. 4,916,191 discloses a graft copolymer prepared from a macromonomer with hydrophilic and fluorinated monomers for dispersion stabilizer in an emulsion polymerization process.
Compared to the related art disclosed above, there exists a need to prepare water soluble graft copolymers in a convenient and economic process. This objective is achieved by the present invention. The resulting copolymers exhibit desired efficacy as paper retention and drainage aids.